A perfusable structure is a structure that enables the passage of a fluid (e.g., a liquid or a gas) through the structure. An example of a perfusable structure is the vascular structure of an organ of an organism (plant, animal, human), such as the vascular structure of the brains or heart of a human or of an animal, or the vascular structure of a gland, e.g., the prostate of a male mammal. Medical imaging techniques based on monitoring the perfusion of a fluid (lymph) through the vessels of a lymphatic system or blood through the blood vessels to an organ or to a tissue are commonly referred to as “perfusion scanning techniques”.
Examples of such perfusion scanning medical imaging techniques are computed tomography (CT) perfusion, magnetic resonance imaging (MRI) perfusion, nuclear medicine (NM) perfusion, ultrasound perfusion imaging, etc.
In CT perfusion imaging, a traceable iodine-containing contrast agent is injected into the blood of a patient. The contrast agent is transported along the vascular system of the patient. As the contrast agent absorbs the X-rays, the dispersion of the contrast agent can be determined, revealing how much blood is preset and how fast the blood is moving by measuring the vascular transit time.
In MR perfusion imaging, a traceable paramagnetic agent is injected into the vascular structure at a certain location, and the agent's dispersion is monitored as the agent's presence changes the relaxivity of the blood plasma in response to an RF (radio frequency) electromagnetic stimulus. Within this context, the term “relaxivity” refers to the ability of the magnetic compounds of the traceable agent to alter the relaxation times of the blood plasma.
In NM perfusion imaging, the traceable agent is a dose of a radioactive material (also referred to as a “radiopharmaceutical” or “radiotracer”) that is introduced into the blood of a patient. The radiation of the radioactive material is detected and provides information about the material's location and dispersion.
In ultrasound perfusion imaging, the traceable agent comprises gas-filed microbubbles that are administered intravenously. Microbubbles are configured to backscatter ultrasound waves to a much higher degree than the surrounding tissue of the body. The backscattered ultrasound waves contain information about the acoustic properties of the structure being investigated and, therefore, about the location of the microbubbles. Doppler-effect measurements provide information about the flow rate (velocity) of the blood. Power-Doppler measurements provide information on blood volume fraction (i.e., the volume of blood in the tissue relative to the total volume of the tissue).
The perfusion-based imaging techniques enable to infer characteristics of the vascular system of a patient from the dispersion of the traceable agent, e.g., the detection of angiogenesis (the development of new blood vessels). As well known, angiogenesis plays an important role in the growth and metastasis of tumors.